Magneto Info

How to keep the Cessna 170 flying and airworthy.

Moderators: GAHorn, Karl Towle, Bruce Fenstermacher

Post Reply
User avatar
170C
Posts: 3182
Joined: Tue May 06, 2003 11:59 am

Magneto Info

Post by 170C »

I need some education! I have a pair of older Bendix mags and have had them overhauled twice, the last time was in 2014 and they now have 231 hours on them. Friday I was flying and my electronic tachometer began to occasionally flash a light that was an indication of a mag problem. Checking the mags showed the left mag was running rough. At cruise engine performance seemed almost normal, but on the ground at 1000 rpms or less, the engine wouldn't run on the left mag. Today I uncowled the engine and discovered that there was an item not attached to the mag. (The item was what I have always thought was a noise filter with the p-lead attached on one end and the other end apparently going to the ignition switch. Someone told me it probably wasn't a noise filter, but rather was a condenser. I always thought the condensers were inside the mags?) I had found a short screw on the floor of my hangar which turned out to be the screw that secured the "item" to the mag. Put the screw back in the small bracket holding the "item" and the left mag operated normally. I don't understand how that "item", while still attached on both ends via wires, has to be physically attached to the mag for it to work. So please educate me on this issue.
OLE POKEY
170C
Director:
2012-2018
User avatar
edbooth
Posts: 498
Joined: Wed Nov 24, 2004 3:03 am

Re: Magneto Info

Post by edbooth »

That is a noise filter Frank and when it came loose it was probably shorting out the "P" lead as it was bouncing around.
Ed Booth, 170-B and RV-7 Driver
User avatar
170C
Posts: 3182
Joined: Tue May 06, 2003 11:59 am

Re: Magneto Info

Post by 170C »

I suspect you are correct Ed. Funny that at cruise power the left mag still worked to some degree, but at low rpm on the ground the left mag would kill the engine. Guessing the filter & its attaching bracket provided a ground for the mag.

Thanks,

Frank
OLE POKEY
170C
Director:
2012-2018
Post Reply